Solid catalyst particles are utilizable for many processes involving the conversion of organic compounds. A particular example of solid catalyst particles comprises solid phosphoric acid which comprises a calcined mixture of an acid of phosphorus and a porous binder material. These solid phosphoric acid catalysts are effective in the polymerization of normally gaseous olefins to form normally liquid hydrocarbons. In addition, solid phosphoric acid catalysts are very useful in catalyzing the alkylation of aromatic hydrocarbons with alkylating agents such as olefins, aliphatic halides, etc. to form useful products.
The catalyst is composed of a support or substrate portion onto which is incorporated an acid fraction for catalytic activity. It is believed that the substrate portion is formed from the silica-phosphoric acid reaction, principally silicon orthophosphate, Si.sub.3 (PO.sub.4).sub.4, silicon pyrophosphate, SiP.sub.2 O.sub.7, as well as derivatives of these compounds. The catalyst is typically prepared by mixing silica with phosphoric acid followed by extrusion and calcination. The reactions are simply illustrated as follows: EQU 3SiO.sub.2 +4H.sub.3 PO.sub.4 .fwdarw.Si.sub.3 (PO.sub.4).sub.4 +6H.sub.2 O EQU SiO.sub.2 +2H.sub.3 PO.sub.4 .fwdarw.SiP.sub.2 O.sub.7 +3H.sub.2 O
The above reactions indicate that the phosphoric acid will react with silica to yield both types of phosphates depending upon stoichiometry and reaction conditions. The silicon orthophosphate can also be dehydrated during drying to give the silicon pyrophosphate, and this is believed to be the alternative mechanism for the silicon pyrophosphate formation. The silicon ortho- to pyrophosphate conversion also depends on factors such as temperature and hydration, as illustrated by the following equations: EQU Si.sub.3 (PO.sub.4).sub.4 +2H.sub.3 PO.sub.4 .fwdarw.3SiP.sub.2 O.sub.7 +3H.sub.2 O EQU Si.sub.3 (PO.sub.4).sub.4 +heat.fwdarw.2SiP.sub.2 O.sub.7 +SiO.sub.2
The preparation of these catalysts is known in the art as, for example, U.S. Pat. No. 2,586,852 which describes a solid phosphoric acid comprising a mixture of kaolin, a crystalline silica and phosphoric acid. Other patents which describe various methods of forming this catalyst composite include U.S. Pat. Nos. 2,650,201, 2,833,727, 2,871,199, and 3,112,350.
One disadvantage which may occur during the use of these catalyst composites during a polymerization or alkylation reaction is that the catalyst particles may tend to disintegrate and form solid beds through which the feedstock encounters difficulty in passage through the catalyst bed. Likewise, the catalyst particle, if not disintegrated, may also possess a tendency to increase in volume or swell due to the deposition of coke thereon, thereby further reducing the space between the particles with attendant difficulty of passage through the bed.
It is therefore apparent that the amount of space between the catalyst particles is important and indeed may be considered critical in nature in order to avoid an excessive pressure drop. Inasmuch as the space between the catalyst particles or voidage is critical it is necessary to provide catalyst particles which will not tend to reduce this voidage but will provide a sufficient amount of voidage to enable any expansion of the catalyst particle without excessive loss of voidage and thereby allow a concurrent stability of pressure to be maintained.
The prior art is replete with patents showing various shaped catalyst particles. However, as will hereinafter be shown in great detail, these particles comprise bases having a catalytically active metal deposited thereon or zeolitic catalysts which may not contain a catalytic metal. Examples of these prior patents include U.S. Pat. No. 3,966,644 which shows a porous hydrotreating catalyst particle comprising a major portion of alumina and a miner portion of silica having a catalytic metal such as molybdenum, cobalt nickel, or mixtures thereof deposited on this catalyst base. U.S. Pat. Nos. 4,328,130 and 4,342,643 show shaped channeled catalysts which comprise a refractory oxide such as alumina, silica, silica-alumina, magnesium, etc. containing active transition metals in the form of metals, metal oxides, metal sulfides, and, if so desired, an aluminosilicate zeolite. U.S. Pat. No. 4,370,492 discloses a carrier such as a silicic acid having a noble metal composited thereof. Likewise, U.S. Pat. No. 4,495,307 also shows a shaped catalyst comprising a catalyst base such as alumina, silica or silica-alumina, having a hydrogenation metal selected from Group VIB and Group VIII of the Periodic Table composited thereon. U.S. Pat. No. 4,391,740 is drawn to a catalyst for hydroprocessing heavy carbonaceous feedstocks in which an elongated extrudate of a catalyst of a base such as alumina or silica having a catalytic metal such as molybdenum, tungsten, nickel or cobalt composited thereon, the preferred shape for this catalyst being oval or elliptical in configuration with or without bumps. U.S. Pat. Nos. 4,394,303, 4,489,173 and 4,606,815 all disclose shaped catalysts for hydroprocessing hydrocarbon feedstocks of lobular configuration, said bases comprising refractory inorganic oxides or clays having a catalytic metal such as molybdenum, tungsten, nickel or cobalt composited thereon. Likewise other shaped catalyst particles having lobular shapes are set forth in U.S. Pat. Nos. 4,028,227, 4,495,307 and 4,534,855. The first of these references utilizes a catalyst base such as alumina impregnated with cobalt and/or molybdenum while the latter two comprise only alumina.
Other prior U.S. patents disclose shaped particles such as U.S. Pat. No. 4,441,990. This patent discloses hollow shaped catalytic extrudates which are essentially rectangular or triangular in cross section. The catalyst particles comprise support materials onto which metals may be added. Particular catalyst particles which are enumerated include alumina or alumina as a support in admixture with a zeolite, and which may contain cobalt, molybdenum oxides, copper or zinc oxides as an added metal. Another prior U.S. Patent is U.S. Pat. No. 2,644,800 which discloses a shaped catalyst having a packed catalytic reactor comprising a plurality of flanges around a central post element, the support comprising a cylindrical metal having a catalyst surface. In addition, U.S. Pat. No. 4,224,185 discloses a formed, shaped solid catalyst in which a solid catalyst particle is admixed with a fibrillatable polyolefin followed by mechanically shearing the mixture to form a mat of catalyst particles which are entrapped in the polyolefin and thereafter mechanically shaping the mat to provide the desired catalyst particles. Likewise, U.S. patents which disclose shaped catalyst particles include U.S. Pat. Nos. 4,652,687 and 4,717,781. These patents show shaped particles which may be polylobular or cylindrical in configuration. However, these particles are utilized as oxidation catalysts and comprise a Group VIII noble metal, a Group IVA metal and a Group IA or IIA metal composited on a metal oxide support such as alumina.
However, to reiterate, it is to be noted that none of the above shaped catalysts comprise a shaped particle which consists of an admixture of an acid of phosphorus with a porous binder, said admixture being formed with a desired configuration, as is the case of the present invention.